As is known, nappies or incontinence pads comprise an absorbent pad, usually made of cellulose fibres enclosed in a soft outer element, consisting on one side of a permeable sheet of “non-woven fabric”, and on the other side of an impermeable sheet of polyethylene. The two sheets are joined to each other along the respective edges, which are suitably shaped and equipped with retaining elastic elements.
In prior art machines the single nappies or incontinence pads are obtained by means of an operation for cutting into pieces a continuous strip of nappies or incontinence pads which are adjacent to each other and still joined one after another.
Relative to their longitudinal axis, the nappies or incontinence pads comprise a front portion and a rear portion, where two fastening and closure elements are usually fixed, said elements designed to guarantee correct and stable positioning of the item around the user's hips.
The fastening and closure elements are generally fed in pairs and applied on the continuous strip of nappies or incontinence pads before the strip is divided into single nappies or incontinence pads.
Patent application BO2007A000431 by the same Applicant describes a machine for making absorbent items of the above-mentioned type.
Said machine comprises a conveyor for feeding the continuous strip of absorbent items to the device for cutting it into the single absorbent items, through a fastening and closure element feed station.
Said elements are formed, arranged in pairs and applied by a unit whose infeed is fed with a continuous web of elastomeric material.
Said unit comprises a cutting element comprising a pair of rollers rotating in opposite directions which are substantially at a tangent to each other, being designed to obtain from the continuous web a succession of pieces, forming trapezoidal fastening elements, by means of a succession of cuts alternating obliquely in opposite directions along the longitudinal axis of the web.
After that operation the web is separated into a continuous succession of pieces which have a trapezoidal shape, with reference to their bases alternately rotated through 180° relative to each other.
Downstream of the cutting element there is a separating roller which spaces out the pieces. For that purpose, the separating roller, substantially at a tangent to a roller of the above-mentioned pair of cutting roller, has a prismatic shape and each of its faces, at an angle to the adjacent faces, is equipped with a suction seat that is substantially rectangular and designed to receive and retain one of the pieces.
Each suction seat can also move with a reciprocating motion parallel with the axis of the separating roller during the latter's rotation and in the opposite direction to the adjacent seats, between the position for receiving a piece and a second position, reached at a position in which it is at a tangent to a roller for forming pairs of fastening elements.
During the transfer between the separating roller infeed and outfeed, the fastening elements consequently pass from the condition in which they are aligned in a single row to a condition in which they are aligned in two rows which are offset relative to each other and consist of trapezoidal pieces arranged so that the larger bases of the pieces of one row are opposite the larger bases of the pieces of the other row.
Finally, the feed unit comprises the above-mentioned roller for forming pairs of fastening elements, which aligns transversally to their direction of feed each fastening element in one row with an adjacent fastening element in the second row.
For that purpose, the pair forming roller comprises two drums which are coaxial, each having a plurality of radial arms separated from each other by equal angles for using respective suction seats to pick up the fastening elements from the separating roller. During the transfer from the station for pick up from the separating roller to the continuous strip feed line, two radial arms relative to two successive pieces which are part of each of the rows perform a relative movement, thus forming a pair aligned transversally to the direction of feed.
The trapezoidal fastening elements are then applied in pairs at their larger bases and according to a predetermined pitch, to the continuous strip of absorbent items.
However, the fastening element feed unit of the type described limits the operating speed of the machine to which it belongs.
This is firstly due to the extreme mechanical complexity of the roller for forming the pairs of fastening elements.
Secondly, in particular at high operating speeds, during relative sliding, transversal to their direction of feed, of the seats of the separating roller, despite its prismatic shape, there may be interference between the edges of the trapezoidal pieces, with the risk that they may become detached from the respective supports.